Getting stronger and faster means sometimes enduring a wee bit of pain. Some consider DOMS, that pain that comes on 12 to 24 hours after a workout, to be a good thing. Sharp, shooting immediate pain, on the other hand, means stop.
Sharp pain while exercising is your body's way of communicating with you that you are doing something it doesn't like. Your body wants and needs you to stop. Listen to this pain; chances are it is in some joint or your lower back area.
If you are strength training, stop and check your technique. Try the motion again a little more slowly and thoughtfully. Same pain? Then try the motion smaller. Same pain? Then stop. You experimented with your options, so stopping does not mean wimping out. In this case, it means you're taking care of yourself. If you work with a trainer, ask him or her to watch your form or suggest an alternative exercise for you to try. The sharp pain generally means you are injuring the tissues in your joint, and trust me, you don't want to damage your soft tissues.
All that being said, to get stronger you do have to push yourself and getting close to maximum effort is going to feel taxing. You have to learn by trial and error when to push yourself, when to ease up, and when to stop.